<nav>    <a [routerLink]="['/']">主页</a>    <a [routerLink]="['/introduction']">简介</a>    <a [routerLink]="['/about']">关于我们</a>    <div *ngIf="nlogin">        <a [routerLink]="['/login']">登录</a>    </div>    <div *ngIf="school">        <a [routerLink]="['/school']">管理学校</a>    </div>    <div *ngIf="college">        <a [routerLink]="['/college']">管理学院</a>    </div>    <div *ngIf="teacher">        <a [routerLink]="['/teacher']">选择学生</a>    </div>    <div *ngIf="student">        <a [routerLink]="['/student']">选择导师</a>    </div></nav>